Color is not the only means used to convey information - Required
There is sufficient contrast between foreground and background text - Required
There is sufficient contrast when color is used to convey information - Strongly Recommended
Colour Contrast Analyser — "a free application available for Windows and Mac where testers can conduct manual color contrast analyses of web content and non-HTML content (e.g., document files, email) and simulate certain visual conditions" - Deque University
Note: Automated color contrast tools may produce false positive and require manual evaluation in some instances. For example, the automated tools cannot identify when a background image or a gradient is used in place of a solid color.